So I put back the hdd to the cloudstor case and used LSrecovery to reset the the device. I can access the device again. And miraculously, the files are still intact! (But I did change the folders name when it was accessed directly as a slave hdd earlier, hence I am not sure if that is why the folders are not being removed)
Here is what happen :
1) Folder name on Cloudstor before it went kaput - "MY BACKUP"
2) Open Cloustor case, remove the HDD
3) Stick the HDD as slave on PC
4) Download Ubuntu to USB and boot up
5) Access the HDD from ubuntu and copy folder "MY BACKUP" to the master HDD
6) Rename "MY BACKUP" on Cloudstor to "DONE - MY BACKUP"
7) Put backup HDD to Cloudstor casing
Run Ls recovery tool
9) "DONE - MY BACKUP" folder was still accessible from Cloudstor as usual and from the network.
I wondered if I did not rename the folder to "DONE - MY BACKUP", would LS recovery would have wipe out the original folders.
Thanks joma90 for all the help!